This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A variety of diseases can be cured by bone marrow or blood transplantation, but this procedure is frequently complicated by a harmful immune reaction of donor cells against the recipient. Previous studies have shown that an agonistic CD28-specific antibody that binds to donor cells can prevent this immune reaction in mice. We have made a similar antibody that binds to human donor cells, but we do not know whether this antibody could prevent the immune reaction after bone marrow or blood transplantation. This antibody also binds to non-human primate donor cells but not against dog or mouse donor cells. The FDA will not allow testing of the antibody in humans, unless prior testing has been done in nonhuman primates to show that the antibody is safe and effective. The pilot study proposed in this application is intended to provide initial information that could be used to assess the merits of further studies with the use of this antibody as a way of preventing immune reactions after bone marrow or blood transplantation. The results of this project showed that the CD28 antibody did not prevent the harmful immune reaction of donor cells against the recipient. The project has been closed.